The present invention broadly relates to an improved electrolyte and process for elecrodepositing zinc alloys, and more particularly, to an improved aqueous acid zinc alloy electrolyte containing an improved additive agent for providing improved grain-refinement, reduced dendrite formation, increased adhesion and ductility and an unexpected increase in the codeposition of one or more alloying metals in the zinc alloy deposit.
Electrolytes incorporating zinc ions in further combination with one or a combination of nickel, cobalt, iron or mixtures thereof have heretofore been used or proposed for use for depositing zinc alloy platings of a decorative or functional type on a variety of substrates such as iron and steel, for example, to provide for improved corrosion resistance, enhance appearance and/or to build up the surface of a worn part enabling refinishing thereof to restore its original operating dimensions. Such zinc alloy electrolytes and processes are in wide-spread commercial use for industrial or functional plating including strip plating, conduit plating, wire plating, rod plating, tube plating, coupling plating, and the like. A continuing problem associated with such prior art zinc alloy electrolytes has been the inability to achieve the desired grain-refinement of the alloy electrodeposit to provide the requisite semi-bright appearance and associated physical properties including adhesion and ductility. A further problem has been the inability to increase the percentage of the alloying metal constituent such as nickel, cobalt and/or iron in the zinc alloy electrodeposit in order to achieve desired physical and chemical properties. The formation of dendrites on the substrate being plated at high current density areas has also been objectionable.
The present invention provides for an improved electrolyte for electrodepositing zinc alloys incorporating an additive agent which provides for improved grain-refinement, a reduction in dendrite formation, increase in adhesion and ductility while further unexpectedly increasing the codeposition of the alloying metal ions achieving a zinc alloy electrodeposit incorporating higher percentages of such alloying elements.